Final answer:
The nurse should first check for kinks in the tubing to ensure that drainage is not obstructed before considering other actions such as replacing or irrigating the tubing.
Step-by-step explanation:
The nurse is assessing a client who is 6 hours postoperative from coronary artery bypass graft surgery and notes that the client's mediastinal tubes are not draining. The appropriate action for the nurse to take at this time would be to check for kinks in the tubing. This is because kinks can obstruct the flow and prevent drainage. Other options, such as replacing the drainage tubing or irrigating the tubing with normal saline, should be considered only after ensuring that there is no simple obstruction. Documentation of the findings is important, but the nurse must first take active measures to address the potential problem.